Study probes link between loss of smell, diseases like Alzheimer's

Psychiatry professor Kim Good looks at diffusion tensor imaging scans at her Halifax lab on Tuesday. Good is part of the Predict Parkinson’s team studying the link between the reduced ability to smell and Parkinson’s disease. (RYAN TAPLIN / Staff)

Nova Scotia researchers are trying to develop an early warning system for diseases like Alzheimer’s and Parkinson’s using people’s sense of smell.

They’re looking for healthy volunteers aged 40 to 75 to take scratch-and-sniff tests to try to identify particular odours.

“It’s been known for quite some time that patients who are diagnosed with either Alzheimer’s disease or Parkinson’s disease, the neurodegenerative type of disorders, if you ask them or if you ask their spouses, they’ll tell you they haven’t been able to smell properly for three, five, sometimes even 10 years before their diagnosis,” said Kim Good, an associate professor in the psychiatry department at Dalhousie University in Halifax.

The sense of smell can deteriorate for a variety of reasons, such as exposure to chemicals.

“Just aging in general deteriorates your sense of smell,” Good said.

But for Alzheimer’s or Parkinson’s patients, the loss of the ability to differentiate smells is often worse than for others the same age.

“We’re trying to amass a very large sample (and then be) able to follow those people, particularly the people who do poorly on the olfactory test,” Good said.

“We think that’s kind of the first step — that’s the canary in the coal mine, if you will. Someone who has an olfactory deficit should be followed up and watched a little more closely.”

The test is simple. Volunteers are sent a scratch-and-sniff multiple choice test in the mail.

“You remember the little patches that kids used to scratch? It’s exactly that same technology,” Good said.

“It’s very simple if you have an intact sense of smell, very, very simple. If you have an impairment in your sense of smell, it’s quite frustrating.”

Good’s team is made up of a fluctuating number of people, mostly from Dalhousie, usually numbering around 12. They come from fields that include neuropsychology and psychiatry.

They are mainly interested in people who do well or poorly on the smell test. These are the subjects who then come into the clinic for cognitive testing, an MRI scan and a sleep study.

“We ask them to come in and we do a special type of brain scan,” Good said.

“So we look at not only how the brain is structurally, but we’re interested in the pathways, the connections between brain regions and a specific area that’s involved in the sense of smell.”

If successful, the work could lead to early intervention for those who might develop Parkinson’s or Alzheimer’s.

Good said disease-modifying drugs could help people who have been diagnosed long before symptoms appear.

“We might be able to intervene early and either stop the disorder or at least slow the progress. We don’t have any disease-modifying drugs at this point, mostly.”

The researchers have used Kijiji to recruit test subjects, but “they’re not coming in as quickly as we would like,” Good said.

Ideally, the group would have 1,200 participants, but at the moment the study involves fewer than 200 people. The plan is to continue the work until 2017, and then a followup study will be conducted if the researchers get more funding.

As the population gets older, more people are being diagnosed with diseases like Alzheimer’s, Good said.

“Because the baby boomers are starting to age into the age range that’s of the highest risk, we are going to be seeing more, absolutely.”

In 2011, there were 747,000 Canadians with Alzheimer’s and other forms of dementia, according to the Alzheimer Society of Canada. It estimates that, if nothing changes, by 2031 that number could grow to 1.4 million.